In the past years, advances in biotechnology have made it possible to produce a variety of proteins for pharmaceutical applications using recombinant DNA techniques. Because proteins are larger and more complex than traditional organic and inorganic drugs (e.g., possessing multiple functional groups in addition to complex three-dimensional structures), the formulation of such proteins poses special problems. For a protein to remain biologically active, a formulation must preserve intact the conformational integrity of at least a core sequence of the protein's amino acids while at the same time protecting the protein's multiple functional groups from degradation. Degradation pathways for proteins can involve chemical instability (e.g., any process which involves modification of the protein by bond formation or cleavage resulting in a new chemical entity) or physical instability (e.g., changes in the higher order structure of the protein). Chemical instability can result from deamidation, racemization, hydrolysis, oxidation, beta elimination or disulfide exchange. Physical instability can result from denaturation, aggregation, precipitation or adsorption, for example. The three most common protein degradation pathways are protein aggregation, deamidation and oxidation. Cleland et al., Critical Reviews in Therapeutic Drug Carrier Systems 10(4): 307-377 (1993).
Included in the proteins used for pharmaceutical applications are antibodies. Stable acqueous formulations have been developed for pharmaceutical antibodies. See, e.g., WO 2011/084750. There is still a need in the art for a stable aqueous pharmaceutical formulation comprising an antibody, such as an anti-VEGF antibody and an anti-CD20 antibody, which mitigates formation of dimers, soluble aggregates, and particulates.
CD20 and Anti CD20 Antibodies
The CD20 molecule (also called human B-lymphocyte-restricted differentiation antigen or Bp35) is a hydrophobic transmembrane protein with a molecular weight of approximately 35 kD located on pre-B and mature B lymphocytes (Valentine, M. A., et al., J. Biol. Chem. 264(19) (1989) 11282-11287; and Einfield, D. A., et al. (1988) EMBO J. 7(3):711-717; Tedder, T. F., et al., Proc. Natl. Acad. Sci. U.S.A. 85 (1988) 208-12; Stamenkovic, I., et al., J. Exp. Med. 167 (1988) 1975-80; Tedder, T. F., et al., J. Immunol. 142 (1989) 2560-8). CD20 is found on the surface of greater than 90% of B cells from peripheral blood or lymphoid organs and is expressed during early pre-B cell development and remains until plasma cell differentiation. CD20 is present on both normal B cells as well as malignant B cells. In particular, CD20 is expressed on greater than 90% of B cell non-Hodgkin's lymphomas (NHL) (Anderson, K. C., et al., Blood 63(6) (1984) 1424-1433)) but is not found on hematopoietic stem cells, pro-B cells, normal plasma cells, or other normal tissues (Tedder, T. F., et al., J. Immunol. 135(2) (1985) 973-979).
The 85 amino acid carboxyl-terminal region of the CD20 protein is located within the cytoplasm. The length of this region contrasts with that of other B cell-specific surface structures such as IgM, IgD, and IgG heavy chains or histocompatibility antigens class I1 a or β chains, which have relatively short intracytoplasmic regions of 3, 3, 28, 15, and 16 amino acids, respectively (Komaromy, M., et al., NAR 11 (1983) 6775-6785). Of the last 61 carboxyl-terminal amino acids, 21 are acidic residues, whereas only 2 are basic, indicating that this region has a strong net negative charge. The GenBank Accession No. is NP-690605. It is thought that CD20 might be involved in regulating an early step(s) in the activation and differentiation process of B cells (Tedder, T. F., et al., Eur. J. Immunol. 16 (8) (1986) 881-887) and could function as a calcium ion channel (Tedder, T. F., et al., J. Cell. Biochem. 14D (1990) 195).
There exist two different types of anti-CD20 antibodies differing significantly in their mode of CD20 binding and biological activities (Cragg, M. S., et al., Blood, 103 (2004) 2738-2743; and Cragg, M. S., et al., Blood, 101 (2003) 1045-1052). Type I antibodies, as e.g. rituximab (a non-afocusylated, non-glycoengineered antibody with normal glycosylation pattern, also named “RTX”), are potent in complement mediated cytotoxicity, whereas type II antibodies, as e.g. Tositumomab (B1), 11B8, AT80 or humanized B-Ly1 antibodies, effectively initiate target cell death via caspase-independent apoptosis with concomitant phosphatidylserine exposure.